1. Field of the Invention
This invention relates to a process for manufacturing a semiconductor device comprising removal of an undesired ruthenium containing metal adhering to a semiconductor substrate.
2. Description of the Related Art
Recently, a high dielectric-constant film such as Ta2O5 has been used in place of a conventional silicon oxide or nitride film as a capacitance insulating film for a DRAM or FeRAM. Such a high dielectric-constant film permits us to ensure a required accumulated capacitance in a small occupied area and to improve a degree of memory-cell integration.
When using such a high dielectric-constant film and polysilicon as an electrode material sandwiching a capacitance film, oxygen is liberated from the high dielectric-constant film during heating a semiconductor device to oxidize the electrode material. There, therefore, exists a dielectric film (silicon oxide film) having a lower dielectric constant than the high dielectric-constant film between the electrode materials, leading to reduction in a capacitance. Thus, when using a high dielectric-constant film, it is important to select a material which does not become an insulating film due to oxidation as an electrode material sandwiching a capacitance film. It is because once a part of an electrode becomes an insulating film by oxidation, it constitutes a part of a capacitance film, resulting in a reduced capacitance. Ruthenium has recently attracted attention as an electrode material meeting the above requirement. Ruthenium is preferable because it retains conductivity even after oxidation, thus does not cause capacitance reduction and is inexpensive.
However, forming an electrode using ruthenium may lead to peeling of a ruthenium containing metal such as ruthenium and ruthenium oxide adhering to the end face or the rear face of a silicon substrate. The peeled metal may adhere to a device forming area or may cause cross contamination between devices or wafers via a carrying system. Recently, a procedure such as forming an electrode film within a narrow hole has been frequently employed for reducing an occupied area for a capacitor. It requires even forming of a thin ruthenium film, so that it is often essential to use CVD exhibiting good coverage as a deposition method, where adhesion of the ruthenium containing metal to the end and/or the rear faces of the silicon substrate becomes more prominent.
A ruthenium containing metal is known as a so-called lifetime killer to a semiconductor device. In particular, it may cause a variety of problems; for example, it adversely affects device operation due to reduction in carrier mobility and varying a threshold voltage of a transistor with time. A ruthenium containing metal is diffused at a higher rate in a silicon substrate than platinum also known as a lifetime killer. A trace amount of the ruthenium containing metal remaining on the silicon substrate surface may give prominent adverse affects on device properties. As described above, an undesired ruthenium containing metal remaining on a silicon substrate surface may deteriorate reliability of a device.
Therefore, when using ruthenium as an electrode material, it is important to remove an undesired ruthenium containing metal by treatment with an etchant. There have been, however, no etchants capable of dissolving and removing a ruthenium containing metal. For example, aqua regia used for forming a platinum electrode may not be used as a remover for a ruthenium containing metal due to its insufficient dissolving ability.
For effectively removing a ruthenium containing metal, a remover for ruthenium must not only dissolve the ruthenium containing metal but also effectively preventing the dissolved ruthenium containing metal from re-adhering to a silicon substrate.
In the light of the above situation, an objective of this invention is to provide a process for manufacturing a semiconductor device comprising depositing a ruthenium film wherein an undesired ruthenium containing metal may be adequately dissolved and removed and re-adhesion of the dissolved ruthenium containing metal may be effectively prevented.
To solve the above problems, this invention provides
[1] a process for manufacturing a semiconductor device, comprising the steps of:
depositing an insulating film in a device forming area on a semiconductor device;
depositing a barrier metal film on the insulating film;
depositing a first ruthenium film on the barrier metal film;
removing a ruthenium containing metal adhering to an area other than the device forming area using a first remover containing (a) at least one compound selected from the group consisting of salts containing chlorate, perchlorate, iodate, periodate, salts containing bromine oxide ion, salts containing manganese oxide ion and salts containing tetravalent cerium ion and (b) at least one acid selected from the group consisting of nitric acid, acetic acid, iodic acid and chloric acid;
removing the residual first remover using a first washing,
sequentially depositing a capacitance insulating film and a second ruthenium film after patterning the first ruthenium film,
removing a ruthenium containing metal adhering to an area other than the device forming area using a second remover containing (a) at least one compound selected from the group consisting of salts containing chlorate, perchlorate, iodate, periodate, salts containing bromine oxide ion, salts containing manganese oxide ion and salts containing tetravalent cerium ion and (b) at least one acid selected from the group consisting of nitric acid, acetic acid, iodic acid and chloric acid; and
removing the residual second remover using a second washing;
[2] a process for manufacturing a semiconductor device, comprising the steps of:
depositing an insulating film in a device forming area on a semiconductor substrate,
depositing a barrier metal film on the insulating film;
depositing a first ruthenium film on the barrier metal film;
removing a ruthenium containing metal adhering to an area other than the device forming area using a first remover containing (a) at least one compound selected from the group consisting of salts containing chlorate, perchlorate, iodate, periodate, salts containing bromine oxide ion, salts containing manganese oxide ion and salts containing tetravalent cerium ion and (b) at least one acid selected from the group consisting of nitric acid, acetic acid, iodic acid and chloric acid;
sequentially depositing a capacitance insulating film and a second ruthenium film after patterning the first ruthenium film,
removing a ruthenium containing metal adhering to an area other than the device forming area using a second remover containing (a) at least one compound selected from the group consisting of salts containing chlorate, perchlorate, iodate, periodate, salts containing bromine oxide ion, salts containing manganese oxide ion and salts containing tetravalent cerium ion and (b) at least one acid selected from the group consisting of nitric acid, acetic acid, iodic acid and chloric acid; and
removing the residual second remover using a second washing;
[3] a process for manufacturing a semiconductor device, comprising the steps of:
depositing an insulating film in a device forming area on a semiconductor substrate,
depositing a barrier metal film on the insulating film;
depositing a first ruthenium film on the barrier metal film;
sequentially depositing a capacitance insulating film and a second ruthenium film after patterning the first ruthenium film,
removing a ruthenium containing metal adhering to an area other than the device forming area using a second remover containing (a) at least one compound selected from the group consisting of salts containing chlorate, perchlorate, iodate, periodate, salts containing bromine oxide ion, salts containing manganese oxide ion and salts containing tetravalent cerium ion and (b) at least one acid selected from the group consisting of nitric acid, acetic acid, iodic acid and chloric acid; and
removing the residual second remover using a second washing;
[4] a process for manufacturing a semiconductor device comprising the step of sequentially forming a lower electrode film, a capacitance insulating film and an upper electrode film in a device forming area on a semiconductor substrate,
wherein the lower and/or the upper electrode films are made of ruthenium and
comprising the steps of after deposing the ruthenium films, removing a ruthenium containing metal adhering to an area other than the device forming area using a second remover containing (a) at least one compound selected from the group consisting of salts containing chlorate, perchlorate, iodate, periodate, salts containing bromine oxide ion, salts containing manganese oxide ion and salts containing tetravalent cerium ion and (b) at least one acid selected from the group consisting of nitric acid, acetic acid, iodic acid and chloric acid; and then removing the residual remover using a washing;
[5] a process for manufacturing a semiconductor device comprising the steps of:
depositing a ruthenium film in a device forming area on a semiconductor substrate, and
spraying on a given area on the semiconductor substrate a remover containing (a) at least one compound selected from the group consisting of salts containing chlorate, perchlorate, iodate, periodate, salts containing bromine oxide ion, salts containing manganese oxide ion and salts containing tetravalent cerium ion and (b) at least one acid selected from the group consisting of nitric acid, acetic acid, iodic acid and chloric acid while rotating the substantially horizontal semiconductor substrate to remove a ruthenium containing metal adhering to an area other than the device forming area.
According to the manufacturing process of this invention, a remover containing the above (a) and (b) components is used so that a ruthenium containing metal can be adequately dissolved and removed and can effectively prevent re-adhesion of the removed ruthenium containing metal.
In the manufacturing process for a semiconductor device of this invention, the remover is used for washing a semiconductor substrate. Unlike using such a liquid in wet etching, a particularly high level of technique is needed for preventing re-adhesion of the removed ruthenium containing metal. According to this invention to solve the problem, synergism in the combination of components (a) and (b) in the remover may realize satisfactory removal of a ruthenium containing metal and high level of prevention of re-adhesion, resulting in adequate washing. The term xe2x80x9can area other than a device forming areaxe2x80x9d includes end and rear faces of a semiconductor substrate and also peripheral areas in the device forming area (see FIG. 1).
A remover used in this invention is made of inexpensive materials and requires a lower etching cost. Furthermore, a technique such as spin washing may be employed to achieve adequate removing performance, resulting in a longer life of the etchant.
The above manufacturing processes [1] to [4] for a semiconductor device comprises, as one characteristic, the step of removing a residual remover using a washing after treatment with a remover. When using the remover having the particular composition, a cerium (IV) nitrate salt may precipitate after removal. In the manufacturing process for a semiconductor device, a washing is used for removing the residual remover. It may effectively prevent cross contamination between devices or wafers due to residual cerium (IV) nitrate to further improve device reliability. It is preferable to use a liquid containing hydrofluoric acid as a washing because it may effectively dissolve and remove the precipitated cerium (IV) nitrate salt and may prevent re-adhesion of the removed cerium (IV) nitrate salt. Examples of a liquid containing hydrofluoric acid include an aqueous solution of hydrofluoric acid and an aqueous solution of nitric acid and hydrofluoric acid. A concentration of hydrofluoric acid may be, for example, 0.1 wt % to 60 wt % both inclusive.
The manufacturing processes [1] to [4] for a semiconductor device form a capacitor on a semiconductor substrate and may be suitably applied to preparation of a DRAM or FeRAM. In general, a manufacturing process for a DRAM or FeRAM requires a higher level of contamination prevention compared with other semiconductor devices. A trace amount of a ruthenium containing metal may be diffused in a silicon substrate, leading to various problems such as deteriorated reliability in operation of a transistor. This invention may achieve a quite high level of contamination prevention (a residual ruthenium level of 109 atoms/cm2) and thus may be particularly suitable for a manufacturing process for a DRAM or FeRAM comprising forming a capacitor.
The manufacturing process [5] for a semiconductor device employs so-called spin washing technique in which a remover is sprayed on a semiconductor substrate while rotating the substantially horizontal substrate. When removing a ruthenium containing metal by spin washing, removal performance of the ruthenium containing metal may be remarkably improved (described later in Examples). Furthermore, temperature dependency of removing performance may be reduced to adequately remove the ruthenium containing metal even at room temperature. Thus, it may eliminates heating an etchant to simplify an ancillary equipment for washing and to increase a life of the etchant.
In the manufacturing process [5] for a semiconductor device, after forming a lower electrode film and before forming a capacitance insulating film, a ruthenium containing metal adhering to an area other than a device forming area on a semiconductor substrate may be removed using a second remover containing (a) at least one compound selected from the group consisting of salts containing chlorate, perchlorate, iodate, periodate, salts containing bromine oxide ion, salts containing manganese oxide ion and salts containing tetravalent cerium ion and (b) at least one acid selected from the group consisting of nitric acid, acetic acid, iodic acid and chloric acid. It may more effectively prevent contamination by the ruthenium containing metal.
In a manufacturing process for a semiconductor device of this invention, when removing a residual second remover using a second washing after removing a ruthenium containing metal with the second remover, the residual cerium (IV) nitrate salt can be removed and additionally an undesired capacitance insulating film adhering to a rear and an end faces of the semiconductor substrate may be simultaneously removed by appropriately selecting the type of the second washing. It may eliminate a step for removing an undesired capacitance insulating film, leading to improvement in productivity. For example, Ta2O5 as a material for a capacitance insulating film and an aqueous solution of hydrofluoric acid as a second washing may be used to simultaneously remove both residual cerium (IV) nitrate salt and Ta2O5. FIG. 7 shows an etching rate for a Ta2O5 film when immersing a silicon substrate having the Ta2O5 film in an aqueous solution of hydrofluoric acid and indicates that as the acid concentration increases, Ta2O5 may be more suitably dissolved.
A washing for removing a residual remover may be a liquid containing hydrofluoric acid; specifically, an aqueous solution of hydrofluoric acid and an aqueous solution of nitric acid and hydrofluoric acid. A concentration of hydrofluoric acid may be, for example, 0.1 wt % to 60 wt % both inclusive. For simultaneously removing a capacitance insulating film such as Ta2O5 as described above, the content of hydrofluoric acid is preferably 20 wt % or more, more preferably 30 wt % or more, most preferably 40 wt % or more.
As described above, a process for manufacturing a semiconductor device of this invention has a characteristic of using a remover containing a cerium (IV) nitrate salt and an acid.
For a composition in which a cerium (IV) nitrate salt and an acid is combined, JP-B 7-7757 and JP-A 11-131263 have described that used as an etchant for preparing a chrome mask used in a lithography process. When preparing the chrome mask, it is necessary to etch a chromium film such that its cross section becomes tapered. It is known that such a taper shape may be suitably formed by conducting wet etching using a composition having the above combination after forming a resist mask on a chromium film because chromium is dissolved by the action of a cerium (IV) nitrate salt while nitric acid peels the resist mask and the chromium film.
These publications have, however, described etching chromium and there are no description for action to a ruthenium containing metal.
JP-A 11-84627 has disclosed a technique for patterning a chromium film and described that ruthenium may be used in place of a chromium film. It has, however, described only dry etching for etching using ruthenium and there are no descriptions for wet-etching ruthenium using an etchant.
As described above, it has been unknown that a combination of a cerium (IV) nitrate salt and a particular acid exhibits excellent performance in removing a ruthenium containing metal and may effectively prevent re-adhesion of the removed ruthenium containing metal. This invention is based on the observation.